1. Field of the Invention
The present invention relates to ceramics, and more particularly to a chemically bonded phospho-silicate ceramic that exhibits high flexural strength, high compression strength, low porosity and permeability to water, sets rapidly at room temperature, has a definable and bio-compatible chemical composition, is easily colored, and a method of producing the same.
2. Description of the Related Art
There is an acute need for a rapid setting pore-free high strength binding material for use in the construction and waste management industries. Traditional cements and ceramics used in these industries have many drawbacks that make those traditional materials less than ideal. For example, traditional cement, such as Portland cement, lacks fracture toughness, is extremely porous and permeable to water, and is very slow in setting. The open porosity of these traditional cement materials makes these materials susceptible to deterioration during the freezing and thawing which occurs in many climates across the United States, Europe and beyond. The expansion and contraction of water within the open pores of these traditional cement materials causes them to break down as they are exposed to extreme temperature fluctuations. Additionally, traditional cements, such as Portland cement, are slow in setting, requiring continuous hydration and attention until the cement material has been properly set, thus adding considerable labor costs to any given project.
The open porosity and thus high water permeability of traditional cement materials also limits the practical use of these materials in waste management and waste encapsulation projects. Highly porous cements are permeable to ground water and allow wastes and toxins to leach out from the encapsulated cement material.
Slightly soluble silicate minerals such as Wollastenite (CaSiO3) and serpentinite (Mg6Si4O10(OH)8), have been used to develop phosphate cements. These phosphate cements are produced by using phosphoric acid, partially neutralized with zinc and aluminum, and then reacted with Wollastenite or serpentine. In spite of the neutralization step, the acid solutions are highly acidic, making them hard to transport to a construction site as a raw material and requiring rigorous safety training for employees in the construction industry, who are used to just adding water to powdered cement. Additionally, the high acidity of these phosphate cements corrodes conventional construction and concrete equipment.
Ceramics are typically less porous than traditional cement, however, traditional ceramics must be fired at extremely high temperatures in order to solidify and cure the ceramic material for practical use. Fired ceramic construction products are expensive, especially if there are large size components. The firing process is not suitable for waste management purposes because waste components volatilize during firing. Resins and other polymer products used as binding materials also provide a less porous product than traditional ceramic materials, however resins are typically expensive to manufacture, their fumes are toxic, and resulting resin products are flammable.
One ceramic material that has had some success as a binding material is the ceramicrete binder. Ceramicrete binders disclosed in our U.S. Pat. Nos. 5,645,518; 5,830,815 and 5,846,894, include compounds such as magnesium potassium phosphate (MgKPO4.6H2O) and newberyite (MgHPO4.3H2O) ceramics. These ceramicrete binders are considerably less porous than conventional cements, are not toxic or flammable, set at a controllable rate, and are a low cost alternative to polymer resins. These ceramicrete binders provide a compression strength comparable to the compression strength exhibited by Portland cement.
It is also known to combine ash with ceramicrete binders, as disclosed in our U.S. Pat. No. 5,830,815, to increase the compression strength to a level two to three times that of the compression strength of Portland cement, The porosity of the ceramicrete ash product is quite low reducing its susceptibility to freeze thaw deterioration and increasing its practical usefulness as a suitable waste encapsulation material that resists permeation of ground water and the leaching of wastes out of the encapsulated ceramicrete ash product. The ceramicrete ash product, however, is not often suitable for architectural uses where many true and subtle colors and shades are desired because the ash product cannot be easily dyed or colored. The ceramicrete ash product is gray or beige depending upon whether fly ash or bottom ash is used. This gray or beige starting color prevents many common architectural colors such as red, yellow, blue, etc., from being achieved, regardless of how much dye or pigment is added to the ash-containing product. Additionally, ash is a mixture of many oxides and silicates and may contain components that are not bio-compatible.
The lack of bio-compatibility in ash containing products, limits the use of those products in the bio-material industries which also have a great need for rapid setting, pore free, high strength binding materials which are also bio-compatible. Only bio-compatible components can make up the binding materials used in dentistry and orthopedics etc. For example, zinc phosphate cements have been used as dental cements because they are dense, hard and also bio-compatible. Zinc phosphate cements, however, are expensive to manufacture and set rapidly, within minutes, making them difficult to work with and produce in any sort of large quantity. For these reasons zinc phosphate cements are not practical for use in construction or waste encapsulation projects as well. Zinc phosphate cements also do not contain calcium phosphates or hydroxyapatite, which are desirable elements for bone tissue growth.
None of the previous binding materials provide a high strength, low porosity, rapid setting, easily colored, bio-compatible chemical composition needed for use in the construction, waste-management, and bio-material industries.
An object of the present invention is to provide a chemically bonded phospho-silicate ceramic that exhibits high flexural and compression strength. The high strength phospho-silicate ceramic of the present invention can reduce the size of load-bearing structures in the construction industry, provide very strong waste encapsuation matrix and provide a high strength biomaterial for use in prosthetics and dentistry.
Another object of the present invention is to provide the new chemically bonded phospho-silicate ceramic exhibiting low porosity and permeability to water, providing a desirable construction material that is resistant to freeze-thaw deterioration during temperature fluctuations, as well as providing an excellent material for waste encapsulation that is resistant to permeation of ground water and leaching from the encapsulation material.
It is another object of the present invention to provide a phospho-silicate ceramic that sets rapidly at room temperature, without the continuous hydration and attention required by traditional cement materials, thus reducing labor costs. Additionally, the low temperature manufacture of the present invention makes the ceramic suitable for the construction, waste management and bio-material industries.
It is another object of the present invention to provide a new chemically bonded phospho-silicate ceramic made from non-toxic, readily available, easily transportable and inexpensive compounds.
It is another object of the present invention to provide a phospho-silicate ceramic having a definite and definable chemical composition, suitable in the bio-material industry where the chemical components must be known to ensure their bio-compatibility before introduction into the human body.
It is yet another object of the present invention to provide a phospho-silicate ceramic that is easily and readily colored to true colors in any variety of shades or hues.
It is yet another object of the present invention to provide a kit for the simple and easy manufacture of the new chemically bonded phospho-silicate ceramic at an industrial site or for home use.
Yet another object of the present invention is to provide a simple and quick method for manufacturing the new chemically bonded phospho-silicate ceramic of the present invention.
According to one aspect of the present invention, the above objects are realized in a phospho-silicate ceramic formed by chemically reacting a monovalent alkali metal phosphate and a sparsely soluble oxide, with a sparsely soluble silicate in an aqueous solution. The preferred sparsely soluble oxide is magnesium oxide, and the preferred sparsely soluble silicate is calcium silicate.
In one embodiment, the monovalent alkali metal phosphate, the sparsely soluble oxide and the sparsely soluble silicate are all in powder form and are combined to form a mixture. The mixture is comprised of 60% sparsely soluble silicate.
According to one aspect of the invention, the above objects are realized in a method of producing a phospho-silicate ceramic comprising the steps of (a) combining a monovalent alkali metal phosphate powder with a sparsely soluble oxide powder in a stochiometric molar ratio of 1:1 to form a binder powder; (b) adding a sparsely soluble silicate powder in a range of 1-80% by weight to the binder powder, to form a mixture;